This coming Sunday in the Baptism of the Lord. John contrasts his baptism with that of Jesus. 

“I am baptizing you with water, but one mightier than I is coming. I am not worthy to loosen the thongs of his sandals. He will baptize you with the holy Spirit and fire…….

The point is not that one baptism is with water, the other in the Holy Spirit and fire (the early church also baptized in water from the beginning), but that John’s baptism is only in water, that is, a ritual sign expressing outwardly what the person must express inwardly. 

The baptism of Jesus will be definitive: it will be an act of God bringing salvation (Holy Spirit) and judgment (fire). The image of fire is expanded by reference to the process of separating wheat from chaff. A “winnowing fan” or shovel tosses the mixture into the air; the heavier kernels of wheat fall to the floor, while the chaff blows away for later burning (Isa 21:10).